import java.util.Arrays;

public class Test {
    public static void main1(String[] args) {
        String string = "a,b";
        System.out.println(string);
    }

    public static void main2(String[] args) {
        String s1 = "Hello";
        String s2 = "heLLO";
// 小写转大写
        System.out.println(s1.toUpperCase());
// 大写转小写
        System.out.println(s2.toLowerCase());
    }

    public static void main3(String[] args) {
        String s1 = "hello";
        char[] arrays = s1.toCharArray();
        System.out.println(s1.toCharArray());
        System.out.println(Arrays.toString(arrays));
    }

    public static void main(String[] args) {
        String s = String.format("%d-%d-%d", 2019, 9,14);
        System.out.println(s);
    }

}
